Work machine

Abstract

Provided is a work machine which suppresses an increase in starting time of a motor while using a motor connection changeover technology. A duty increase rate in startup control of a motor 340, when a motor drive operation is performed on a trigger switch 1306 in an unloaded condition, is set as a first duty increase rate in the case where a coil connection method is a delta connection, and is set as a second duty increase rate in the case where the coil connection method is a star connection. A calculation unit 50 is configured to control so that the second duty increase rate is larger than the first duty increase rate. The increase rate of the motor rotation speed when the trigger switch 1306 is operated in the unloaded condition is the same in the cases of both the delta connection and the star connection.

Description

Work equipment

[0001] The present invention relates to a work machine.

[0002] 2. Description of the Related Art There is known a technology (motor connection switching technology) that enables driving suited to a task by changing the connection method of the motor coils.

[0003] Patent Document 1 describes an electric power tool as a work machine in which the wiring method of the motor coil can be switched depending on the type of power source (power source voltage) to be connected.

[0004] Patent Document 2 describes an electric power tool as a work machine in which the motor windings are star-connected (Y-connected) and the number of series or parallel connections of the coils in the star connection can be changed depending on the workload applied to the motor. It also describes that when switching the winding connections, a period is set during which the connection changes are repeated, thereby suppressing sudden changes in torque and rotation speed.

[0005] Patent Document 3 describes a motor control for an automobile that can switch between star connection and delta connection.

[0006] JP 2017-121158 A JP 2013-111734 A JP 5-003694 A

[0007] The present inventors have recognized that the following challenges exist when introducing motor connection switching technology into a work machine. - Challenge 1: To provide a work machine that uses motor connection switching technology to prevent the motor from stopping unexpectedly during work. - Challenge 2: To provide a work machine that uses motor connection switching technology to prevent a decrease in work speed. - Challenge 3: To provide a work machine that uses motor connection switching technology to prevent an increase in the motor startup time. - Challenge 4: To provide a work machine that uses motor connection switching technology to prevent an increase in the time it takes for the motor to reach the set rotation speed. - Challenge 5: To provide a work machine that uses motor connection switching technology to provide a good feeling at startup. - Challenge 6: To provide a work machine that uses motor connection switching technology to prevent an increase in reaction force at startup.

[0008] The present invention aims to solve at least one of the above problems 1 to 6.

[0009] One aspect of the present invention is a work machine including a motor having multiple windings, a drive unit having switching elements and driving the motor, a connection switching unit capable of switching the connection method of the multiple windings between a first connection method for high rotation and a second connection method for high torque, a control unit that controls the drive unit and the connection switching unit, and an operation unit that starts and stops the motor, wherein the control unit is configured to control the increase rate, which is the amount of increase per unit time of the duty of a PWM signal applied to the switching elements when starting to drive the motor, so that the increase rate is greater when the motor is in the second connection method than when the motor is in the first connection method.

[0010] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a drive unit having a switching element for driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for starting and stopping the motor, wherein the control unit is configured to control the rate of increase in the rotation speed of the motor when driving of the motor to be greater when the second wiring method is used than when the first wiring method is used.

[0011] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a drive unit having switching elements and driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit controlling the drive unit and the connection switching unit, and an operation unit operating to start and stop the motor, wherein the control unit is configured to start driving the motor in a plurality of drive modes in which the increase rate of the duty of a PWM signal applied to the switching elements or the increase rate of the motor rotation speed differs before and after the switching of the connection method during a single motor drive operation on the operation unit.

[0012] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a drive unit having switching elements for driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for starting and stopping the motor, wherein the control unit is configured to control at least one of an advance angle of a voltage applied to the motor and a conduction angle of the motor so that the advance angle is larger when the motor is in the first connection method than when the motor is in the second connection method.

[0013] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a tool holder driven by the motor, a drive unit having a switching element for driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for starting and stopping the motor, wherein the control unit is configured to control a duty increase rate, which is an increase per unit time in the duty of a PWM signal applied to the switching element, so that the duty increase rate is greater in the second connection method than in the first connection method when the operation unit is operated to start the motor in a no-load state in which no load is applied to the tool attached to the tool holder.

[0014] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a tool holder driven by the motor, a drive unit having a switching element for driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for operating start and stop of the motor, wherein the control unit switches the first connection method and the second connection method when the operation unit is operated in a no-load state where no load is applied to the tool attached to the tool holder. The motor is configured to be able to be started by one of the second wiring methods, and when the operation unit is operated in the no-load state, the control unit is configured to control a duty increase rate, which is an increase per unit time of the duty of the PWM signal applied to the switching element, to a first duty increase rate when the motor is started by the first wiring method, and to a second duty increase rate when the motor is started by the second wiring method, so that the second duty increase rate is greater than the first duty increase rate.

[0015] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a tool holder driven by the motor, a drive unit having a switching element and driving the motor, a connection switching unit capable of switching the connection type of the plurality of windings between a first connection type for high rotation and a second connection type for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for starting and stopping the motor, wherein the control unit is configured to start the motor using one of the first connection type or the second connection type when the operation unit is operated in a no-load state where no load is applied to the tool attached to the tool holder, and the control unit is configured to control the operation unit in the no-load state so that the time from when the operation unit is operated until the duty of the PWM signal applied to the switching element increases to a predetermined value is shorter in the second connection type than in the first connection type.

[0016] Another aspect of the present invention is a work machine comprising: a motor having a plurality of windings; a tool holder driven by the motor; a drive unit having a switching element for driving the motor; a connection switching unit capable of switching the connection type of the plurality of windings between a first connection type for high rotation and a second connection type for high torque; a control unit for controlling the drive unit and the connection switching unit; and an operation unit for starting and stopping the motor, wherein the control unit is configured to start the motor using one of the first connection type and the second connection type when the operation unit is operated in a no-load state in which no load is applied to the tool attached to the tool holder, and the control unit is configured to control the drive unit so that a rotation speed increase rate, which is an increase in the motor rotation speed per unit time, is equal between the first connection type and the second connection type when the operation unit is operated in the no-load state.

[0017] Another aspect of the present invention is a work machine including a motor having a plurality of windings, a tool holder driven by the motor, a drive unit having a switching element for driving the motor, a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque, a control unit for controlling the drive unit and the connection switching unit, and an operation unit for operating start and stop of the motor, wherein the control unit can start the motor using one of the first connection method and the second connection method when the operation unit is operated in a no-load state where no load is applied to the tool attached to the tool holder. The control unit is configured to control a duty increase rate, which is an increase per unit time of the duty of the PWM signal applied to the switching element, so that when the operation unit is operated to start the motor in a no-load state where no load is applied to the tool attached to the tool holder, the duty increase rate is larger in the second wiring method than in the first wiring method, and when the operation unit is operated in the no-load state, the rotation speed increase rate, which is an increase per unit time of the rotation speed of the motor, is equal between the first wiring method and the second wiring method.

[0018] Another aspect of the present invention is a work machine comprising: a motor having a plurality of windings, a tool holder driven by the motor, a drive unit having a switching element and driving the motor, a switch unit capable of changing the internal resistance of the plurality of windings, a control unit for controlling the drive unit and the connection switch unit, and an operation unit for starting and stopping the motor, wherein the control unit is configured to start the motor in one of a first state in which the internal resistance is low and a second state in which the internal resistance is high when the operation unit is operated in a no-load state in which no load is applied to the tool attached to the tool holder, and the control unit is configured to control, when the operation unit is operated in the no-load state to start the motor, a duty increase rate, which is an increase per unit time in the duty of a PWM signal applied to the switching element, so that the duty increase rate is higher in the second state than in the first state.

[0019] The present invention may be expressed as an "electric working machine," "electric tool," "electrical equipment," etc., and such expressions are also valid as aspects of the present invention.

[0020] According to the present invention, at least one of the above problems 1 to 6 can be solved.

[0021] 1 is a perspective view of a work machine 5 according to a first embodiment of the present invention, as seen from above. A perspective view of the work machine 5, as seen from above with a portion of a housing 1320 of the work machine 5 removed. A front view of the work machine 5. A side view of the work machine 5, as seen from the side with a portion of a housing 1320 of the work machine 5 removed. A perspective view showing a state in which the motor housing 1321 and the control board 1311 have been removed in FIG. 2. A cross-sectional view of a motor 340 of the work machine 5. An external view of an operation panel 1316 of the work machine 5. A circuit block diagram of the work machine 5. A simplified graph showing the relationship between the torque and rotation speed of the motor 340 when the motor 340 is of low rotation specification. A simplified graph showing the relationship between the effective current value and torque of the motor 340 when the motor 340 is of low rotation specification. A simplified graph showing the relationship between the torque and rotation speed of the motor 340 when the motor 340 is of high rotation specification. A simplified graph showing the relationship between the effective current value and torque of the motor 340 when the motor 340 is of high rotation specification. 1. A graph showing the relationship between the product torque and saw blade rotation speed of the working machine 5. A control flowchart for the working machine 5. A graph showing the relationship between the motor torque and motor rotation speed of the working machine 5, relating to the second embodiment of the present invention, when the pushing load of the working machine 5 against the mating material is gradually increased in each of the automatic switching mode and the tenacity mode. A graph showing the relationship between the saw blade torque and saw blade rotation speed of the working machine 5, when the pushing load of the working machine 5 against the mating material is gradually increased in each of the automatic switching mode and the tenacity mode. A graph showing the relationship between the saw blade torque and saw blade rotation speed of the working machine 5, when the pushing load of the working machine 5 against the mating material is gradually increased and then decreased in the automatic switching mode. A graph showing the relationship between the battery current effective value of the working machine 5 and the saw blade rotation speed, when the pushing load of the working machine 5 against the mating material is gradually increased and then decreased in the automatic switching mode. A control flowchart for the automatic switching mode of the working machine 5, when the pushing load of the working machine 5 against the mating material is gradually increased after the trigger switch 1306 is turned on. 1 is a control flowchart for an automatic switching mode of the work implement 5, in which the pushing load of the work implement 5 against the mating member is reduced during operation in star connection. 2 is a control flowchart for a tenacity mode of the work implement 5. 3 is a flowchart for overload protection control of the work implement 5.10 is a flowchart of protection control in response to a discharge stop signal from the battery pack 1307 of the work machine 5.

[0033] FIG. 10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the duty of the PWM signal applied to each switching element of the inverter circuit 64, for a control example 1 of the work machine according to embodiment 3 of the present invention.

[0034] FIG. 10 is a flowchart of control example 1 of embodiment 3.

[0035] FIG. 10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, the duty of the PWM signal applied to each switching element of the inverter circuit 64, and the electrical advance angle of the voltage applied to the motor 340, along with time variations in control example 1, for control example 2 of the work machine according to embodiment 3.

[0036] FIG. 10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, the duty of the PWM signal applied to each switching element of the inverter circuit 64, and the electrical advance angle of the voltage applied to the motor 340, along with time variations in control example 1, for control example 3 of the work machine according to embodiment 3.

[0037] FIG. 10 is a flowchart of control example 3 of embodiment 3. 10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the duty of the PWM signal applied to each switching element of the inverter circuit 64 in comparative control example 1 of embodiment 3. A graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the duty of the PWM signal applied to each switching element of the inverter circuit 64 in comparative control example 2 of embodiment 3, along with time variations in control example 1. A graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the duty of the PWM signal applied to each switching element of the inverter circuit 64 when the trigger switch 1306 is operated to drive the motor in a no-load state in each of the automatic switching mode and the tenacity mode (high torque mode) for control example 1 of the work machine of embodiment 4 of the present invention. A flowchart of control example 1 of embodiment 4. Graphs showing the time changes in the rotation speed of the motor 340, the output current of the battery pack 1307, and the electrical advance angle of the voltage applied to the motor 340 when the trigger switch 1306 is operated to drive the motor in an unloaded state in each of the automatic switching mode and the tenacity mode (high torque mode) for Example 2 of the control of the work machine of Embodiment 4.10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the conduction angle of the motor 340 when the trigger switch 1306 is operated to drive the motor in an unloaded state in each of the automatic switching mode and the tenacity mode (high torque mode), for a control example 3 of the work machine of embodiment 4.

[0034] FIG. 10 is a graph showing time variations in the rotation speed of the motor 340, the output current of the battery pack 1307, and the duty of the PWM signal applied to each switching element of the inverter circuit 64 when the trigger switch 1306 is operated to drive the motor in an unloaded state in each of the automatic switching mode and the tenacity mode (high torque mode), for a comparative control example of embodiment 4.

[0035] FIG. 10 is an explanatory diagram of two-phase resistance (internal resistance) in a delta connection.

[0036] FIG. 10 is an explanatory diagram of two-phase resistance (internal resistance) in a star connection.

[0037] FIG. 10 is an explanatory diagram of two-phase resistance (internal resistance) in a configuration in which the number of coils connected in series in each phase in a star connection is variable.

[0022] (Embodiment 1) Figures 1 to 14 relate to a work machine 5 according to a first embodiment of the present invention. Figure 3 defines the mutually orthogonal up-down and left-right directions of the work machine 5. The left-right direction is a direction parallel to the axial direction of the motor shaft 341 of the work machine 5. Figure 4 defines the left and right directions orthogonal to up-down as front and back, respectively. The work machine 5 is a portable circular saw. The work machine 5 includes a housing 1320.

[0023] The housing 1320 is, for example, a resin molded body, and includes a motor housing 1321 that houses the motor 340 and the like, a handle housing 1322 that is gripped by the operator, and a battery attachment section 1323 .

[0024] The motor housing 1321 is a cylindrical part whose central axis is approximately parallel to the left-right direction. The handle housing 1322 extends obliquely in the front-to-back and up-down directions above the right part of the motor housing 1321. A trigger switch 1306 is provided at the top end of the handle housing 1322 as an operation part that allows the user to start and stop the motor 340.

[0025] A metal gear case (saw cover) 1325 is connected to the left side of the handle housing 1322. The gear case 1325 houses a reduction mechanism (not shown) and covers the upper half of the saw blade 1309 as the tool tip.

[0026] The battery attachment section 1323 extends leftward from the rear end of the handle housing 1322, and allows the battery pack 1307 to be detachably attached. The work machine 5 is powered by the battery pack 1307 and operates on the power of the battery pack 1307. The work machine 5 has an operation panel 1316 on the top surface of the battery attachment section 1323. The user can switch the operation mode of the work machine 5 using the operation panel 1316.

[0027] A hook 1324 is attached to the front of the handle housing 1322, and is configured so that the work implement 5 can be hooked onto a hooked portion. The hook 1324 is attached to the housing 1320 so as to be rotatable. In addition, a sub-handle 1326 is provided above the motor housing 1321. The sub-handle 1326 is a part that the operator grips during work.

[0028] The work machine 5 has a motor 340 inside a motor housing 1321. The rotation of the motor 340 is reduced by a reduction mechanism inside a gear case 1325 and transmitted to the saw blade 1309. The saw blade shaft provided on the output side of the reduction mechanism, the bolts that fix the saw blade 1309 to the saw blade shaft, etc. constitute a tool tip holder.

[0029] 6 , the motor 340 is an inner rotor brushless motor and includes a motor shaft 341 (output shaft), a rotor core 342, a rotor magnet 343 (permanent magnet), a stator core 344, and a stator coil 345.

[0030] The rotor core 342 is provided around the motor shaft 341 and rotates integrally with the motor shaft 341 relative to the stator core 344. There are four rotor magnets 343, which are inserted and held at 90-degree intervals in the circumferential direction in the rotor core 342. The rotor cores 342 and the rotor magnets 343 constitute the rotor of the motor 340.

[0031] The stator core 344 is arranged to surround the outer periphery of the rotor core 342. The stator core 344 includes a cylindrical (annular) yoke portion 346 and six teeth 347 (teeth portions) that protrude radially inward from the yoke portion 346. A stator coil 345 is provided on each tooth 347. Each tooth 347 forms a winding slot. The stator core 344 and the stator coil 345 form a stator of the motor 340. The stator coil 345 forms multiple windings of the motor 340.

[0032] The work machine 5 has a control board 1311 (FIG. 2) inside the motor housing 1321 and multiple battery connection terminals (not shown) inside the battery mounting section 1323. The control board 1311 is equipped with circuits such as the calculation unit 50, control power supply circuit 51, inverter circuit 64, etc., which will be described later. The multiple battery connection terminals face below the battery mounting section 1323. The multiple battery connection terminals come into contact with terminals of the battery pack 1307 mounted in the battery mounting section 1323 and are electrically connected thereto.

[0033] As shown in FIG. 2 , the work machine 5 has a relay board 30 inside the motor housing 1321. The relay board 30 is mounted with a plurality of relay elements 31. The plurality of relay elements 31 constitute a relay unit. The plurality of relay elements 31 are an example of a connection switching unit that can switch the wiring method of the stator coil 345 (hereinafter referred to as the "coil wiring method") between a first wiring method for high rotation and a second wiring method for high torque, that is, a connection switching unit configured to be able to switch between a high rotation speed connection state in which the plurality of windings are connected to each other so as to have a high rotation speed characteristic, which is a characteristic that the rotation speed is higher than other characteristics, and a high torque connection state in which the plurality of windings are connected to each other so as to have a high torque characteristic, which is a characteristic that the torque is higher than other characteristics.

[0034] The relay board 30 is attached to the motor 340 with screws or the like. The relay board 30 faces a vent hole provided in the motor housing 1321.

[0035] As shown in FIG. 7, the operation panel 1316 is provided with an operation mode changeover switch 312, an operation mode display LED 313, a light mode changeover switch 314, and light mode display LEDs 315 and 317.

[0036] The operation mode changeover switch 312 is an operation mode changeover unit (mode selection unit) that allows the operator to change the operation mode of the work machine 5 between an automatic changeover mode (first mode) and a tenacious mode (second mode). The operation mode display LED 313 is an operation mode display unit that displays the current operation mode, and is turned off in the automatic changeover mode and turned on in the tenacious mode, for example.

[0037] The light mode selector switch 314 is a light mode switching unit that allows the operator to switch the light mode of the work machine 5. The light modes include, for example, a constant light mode and a trigger operation light mode in which the light is turned on only when the trigger switch 1306 is pulled. The light mode display LED 315 is turned on in the trigger operation light mode and is turned off in the constant light mode. The light mode display LED 317 is turned on in the constant light mode and is turned off in the trigger operation light mode.

[0038] FIG. 8 is a circuit block diagram of the work machine 5.

[0039] The battery pack 1307 includes a battery cell 67 and a protection IC 68. The protection IC 68 functions as a battery-side control unit, and outputs a discharge stop signal (LD signal) when the discharge current from the battery cell 67 exceeds a battery-side overcurrent protection threshold.

[0040] The inverter circuit 64 is a drive unit that is made up of six switching elements connected in a three-phase bridge and drives the motor 340. Each switching element of the inverter circuit 64 is, for example, an FET or an IGBT, and is an example of a heat generating element that constitutes the work machine 5. The inverter circuit 64 is provided between the output terminals of the battery pack 1307. The detection resistor 65 is provided in the path of the current (hereinafter referred to as "motor current") that flows through the stator coil 345. The inverter circuit 64 is mounted on the control board 311.

[0041] The control power supply circuit 51 converts the output voltage of the battery pack 1307 into a power supply voltage for the calculation unit 50 and supplies it to the calculation unit 50. The current detection circuit 52 detects the motor current from the voltage across the detection resistor 65 and sends it to the calculation unit 50 as a control unit. The switch operation detection circuit 53 detects the operation of the trigger switch 1306 and sends it to the calculation unit 50. The battery type detection circuit 54 detects the type of the battery pack 1307 (rated voltage, rated capacity, etc.) from the voltage of an identification terminal (not shown) of the battery pack 1307 and sends it to the calculation unit 50. The battery type detection circuit 54 constitutes a detection unit that detects the capacity of the power source. The voltage detection circuit 55 detects the output voltage of the battery pack 1307 (hereinafter referred to as "battery voltage") and sends it to the calculation unit 50.

[0042] The LD detection circuit 66 detects a discharge stop signal (LD signal) from the battery pack 1307 and transmits it to the calculation unit 50. The calculation unit 50 and each circuit such as the control power supply circuit 51 are mounted on a control board 311.

[0043] The control signal circuit 56 outputs control signals that control the on / off of each switching element of the inverter circuit 64 under the control of the calculation unit 50. The rotational position detection circuit 57 detects the rotational position of the motor 340 based on the output signal of a Hall IC (magnetic sensor) 63 provided near the rotor magnet 343 and transmits the detected signal to the calculation unit 50. The rotation speed detection circuit 58 detects the rotation speed of the motor 340 (hereinafter referred to as "motor rotation speed") based on the output signal of the rotational position detection circuit 57 and transmits the detected signal to the calculation unit 50. In this specification, "rotation speed" refers to the number of rotations per unit time and represents the rotation speed. The operation mode detection circuit 59 detects the operation mode (operation mode) in response to the user's operation of the operation mode switch 312 and transmits the detected signal to the calculation unit 50. The illumination LED drive circuit 61 drives the illumination LED 62 under the control of the calculation unit 50.

[0044] The calculation unit 50 is a control unit that includes a microcontroller or the like and controls the overall operation of the work machine 5. The calculation unit 50 controls the drive of the inverter circuit 64 via the control signal circuit 56 (for example, PWM control of each switching element of the inverter circuit 64) and controls the drive current supplied to the stator coil 345. The calculation unit 50 can detect the torque of the motor 340 (hereinafter referred to as "motor torque"), i.e., the load applied to the motor 340 (hereinafter referred to as "work load"), from the motor current.

[0045] The calculation unit 50 controls the relay element 31 to switch the coil connection method (coil connection) between a delta connection for high rotation speeds and a star connection (Y connection) for high torque. The delta connection state of the coil connection method corresponds to a high rotation speed connection state, and the star connection state of the coil connection method corresponds to a high torque connection state. The calculation unit 50 can execute connection switching control to switch the coil connection method from the delta connection to the star connection, that is, connection switching control to switch from a high rotation speed connection state to a high torque connection state.

[0046] The plurality of relay elements 31 include three delta connection relay elements 32 as a first relay unit and three star connection relay elements 33 as a second relay unit. The calculation unit 50 sets the coil connection method to delta connection by turning on the delta connection relay elements 32 and turning off the star connection relay elements 33, and sets the coil connection method to star connection by turning on the star connection relay elements 33 and turning off the delta connection relay elements 32. Note that the number of star connection relay elements 33 may be two. In other words, one of the three star connection relay elements 33 may be replaced with a short circuit.

[0047] The operation modes of the work machine 5 (control modes by the calculation unit 50) include an automatic switching mode (first mode) and a tenacious mode (second mode). As described above, the operator can select the operation mode using the operation mode changeover switch 312.

[0048] In the automatic switching mode (first mode), the calculation unit 50 switches the coil connection method from a delta connection (first connection method) for high rotation to a star connection (second connection method) for high torque in response to an increase in the workload. That is, in the automatic switching mode, the calculation unit 50 is configured to control the multiple relay elements 31 so that the coil connection method is switched from the high rotation mode to the high torque mode when the workload increases.

[0049] In the tenacity mode (second mode), the calculation unit 50 does not switch the coil wiring method from a high-speed connection to a high-torque connection, regardless of an increase in the work load. Specifically, in the tenacity mode, the calculation unit 50 fixes the coil wiring method to a star connection, which is for high torque, and does not switch the coil wiring method regardless of the work load. The work load is the load applied to the motor 340 by work, i.e., the load applied to the motor 340 when the rotating saw blade 1309 is pressed against the mating material, and does not include temporary high loads associated with starting the motor 340. That is, in the tenacity mode, the calculation unit 50 maintains the wiring method as the second wiring method.

[0050] The automatic switching mode will be described below in this embodiment.

[0051] Figure 9 is a graph showing the relationship between motor torque and motor rotation speed, with the horizontal axis representing motor torque and the vertical axis representing motor rotation speed, when the motor 340 is a low-speed specification. Figure 10 is a graph showing the relationship between motor torque and motor rotation speed, with the horizontal axis representing the effective value of motor current and the vertical axis representing motor torque. When the motor 340 is a low-speed specification, the delta connection is switched to the star connection at the intersection of the delta connection characteristic line and the star connection characteristic line (the winding switching point in Figure 9). Because the effective value of the motor current at the torque at the intersection is smaller than the overcurrent protection threshold, the overcurrent protection will not be activated before the connection is switched. However, there is an issue that the low motor rotation speed results in slow operating speed.

[0052] 11 and 12 show the relationship between motor torque and motor speed, and the relationship between the effective value of motor current and motor torque, respectively, when the motor 340 is configured for high-speed rotation, which is suitable for high rotation. The motor 340 can be configured for high rotation by, for example, reducing the number of turns of the stator coil 345, thereby improving operating speed. On the other hand, with a high-speed rotation specification, the motor current increases significantly compared to a low-speed rotation specification for the same torque. The effective value of the motor current at the intersection of the delta-connection characteristic line and the star-connection characteristic line exceeds the overcurrent protection threshold. For this reason, with a high-speed rotation specification, it is difficult to switch from a delta connection to a star connection at the intersection of the delta-connection characteristic line and the star-connection characteristic line (switching point 2 in FIG. 11 ). Therefore, with a high-speed rotation specification, the delta-connection to the star-connection is switched at switching point 1, where the torque is lower than at the intersection of the delta-connection characteristic line and the star-connection characteristic line. The time from the start to the completion of the wiring changeover is very short, for example, 100 ms or less, and it is important from the viewpoint of the working feel to appropriately switch on and off the relay element 31 and the inverter circuit 64 during this time. This point will be described later.

[0053] FIG. 13 is a graph showing the relationship between the product torque of the work machine 5 (torque of the saw blade 1309) on the horizontal axis and the rotational speed of the saw blade 1309 (saw blade rotation speed) on the vertical axis. Note that FIG. 13 illustrates an example in which the motor 340 is controlled at a constant speed in the low torque range, and the saw blade rotation speed is constant in the low torque range. A graph showing the relationship between torque and rotation speed of the tool bit can be obtained by the following experiment. A load device is connected to the output shaft holding the tool bit, and the rotational speed and torque of the output shaft are measured while the load torque generated by the load device is gradually increased from zero. The results are output as a graph with the torque of the output shaft on the horizontal axis and the rotational speed of the output shaft on the vertical axis. In many work machines, the motor and the output shaft holding the tool bit are connected via a reduction gear mechanism, so the torque and rotational speed of the motor can be calculated from the torque and rotational speed of the output shaft holding the tool bit and the reduction ratio of the reduction gear mechanism. Therefore, a graph showing the relationship between motor torque and rotational speed can also be obtained by an experiment similar to the above.

[0054] The no-load rotation speed of the saw blade 1309 in star connection shown in Figure 13 is the no-load rotation speed of the saw blade 1309 when it is assumed that the inverter circuit 64 is controlled at 100% duty in a no-load state and in a star connection state, and is the saw blade rotation speed (approximately 3,000 min-1, for example) indicated by the intersection of an extension line (approximate curve) of the star connection characteristic line in Figure 13 and a straight line indicating zero torque. The motor rotation speed corresponding to the no-load rotation speed of the saw blade 1309 in star connection is the no-load rotation speed of the motor 340 in star connection (hereinafter referred to as the "no-load rotation speed in star connection"). In the work machine 5, the calculation unit 50 starts connection switching control to switch the coil connection from delta connection to star connection when the coil connection is delta connection and the motor rotation speed is higher than the no-load rotation speed in star connection. Therefore, compared to when connection switching control is started when the motor rotation speed is lower than the no-load rotation speed in star connection, motor 340 can be configured to a higher rotation speed specification, while preventing motor 340 from stopping due to overcurrent protection before connection switching control is started.

[0055] 14 is a control flowchart for the work machine 5. When the trigger switch 1306 is turned on (S201), the calculation unit 50 turns on the delta connection relay element 32 (S203), turns off the star connection relay element 33 (S205), starts driving the inverter circuit 64 (S207), and drives the motor 340 (operates the work machine 5) with the coil connection method set to delta connection (S209). If the workload does not exceed threshold A (No in S211), the calculation unit 50 continues driving the motor 340 in the delta connection.

[0056] When the workload exceeds threshold A (Yes in S211), the calculation unit 50 stops driving the inverter circuit 64 (S213) and sends an OFF signal to the delta connection relay element 32 (S215). This turns the delta connection relay element 32 OFF (S217). The calculation unit 50 waits until the motor rotation speed falls below the no-load speed for star connection (No in S219). When the motor rotation speed falls below the no-load speed for star connection (Yes in S219), the calculation unit 50 sends an ON signal to the star connection relay element 33 (S221). This turns the star connection relay element 33 ON (S223). The calculation unit 50 resumes driving the inverter circuit 64 (S225) and drives the motor 340 with the coil connection method set to star connection (S227). In the case of the fifth control, S227 becomes constant speed control.

[0057] This embodiment has the following advantages.

[0058] (1) The calculation unit 50 starts connection switching control, which switches the coil connection method from delta connection to star connection, when the motor rotation speed is higher than the no-load rotation speed for star connection. Therefore, compared to when connection switching control is started when the motor rotation speed is lower than the no-load rotation speed for star connection, it is possible to keep the motor 340 in a high-speed rotation specification while preventing the motor 340 from stopping due to overcurrent protection before the start of connection switching control.

[0059] (2) In the connection switching control, the calculation unit 50 switches the inverter circuit 64 to a drive stop state and switches all of the relay elements 31 to an open connection state (connection cut state). Therefore, compared to a case where the connection is switched from a state in which the delta connection relay element 32 is on and the star connection relay element 33 is off (a high rotation speed connection state) to a state in which the delta connection relay element 32 is off and the star connection relay element 33 is on (a high torque connection state) without an open connection state (connection cut state) in between, the risk of a short-circuited connection state in which both relay elements 31 and 32 are on is reduced, and the risk of a decrease in motor rotation speed and damage to the star connection relay element 33 is reduced.

[0060] (3) In the connection switching control, when the inverter circuit 64 is in a drive-stop state, the calculation unit 50 is configured to switch the state from one in which the delta connection relay element 32 is on and the star connection relay element 33 is off (high rotation speed connection state) to one in which both the delta connection relay element 32 and the star connection relay element 33 are off (connection interruption state). Therefore, the delta connection relay element 32 is turned off when no current is flowing through it, which reduces the risk of damage to the delta connection relay element 32 compared to when the delta connection relay element 32 is turned off when current is flowing through it.

[0061] (4) In the connection switching control, when the inverter circuit 64 is in a drive-stop state, the calculation unit 50 is configured to switch the state in which the delta connection relay element 32 and the star connection relay element 33 are both OFF (connection interruption state) to a state in which the delta connection relay element 32 is OFF and the star connection relay element 33 is ON (high-torque connection state). Therefore, no current flows through the star connection relay element 33 at the moment the star connection relay element 33 is turned ON, thereby reducing the risk of damage to the star connection relay element 33.

[0062] 1 to 8 and 15 to 23 relate to a second embodiment of the present invention. Below, descriptions of parts common to the first embodiment will be omitted as appropriate. In this embodiment, differences between the automatic switching mode and tenacity mode of the work implement 5 will be mainly described.

[0063] Figure 15 is a graph showing the relationship between the motor torque and motor rotation speed of the work implement 5, and is a graph showing the relationship when the pressing load of the work implement 5 against the opposing material (hereinafter referred to as the "work implement pressing force") is increased in both the automatic switching mode and the tenacity mode.

[0064] In automatic switching mode, the calculation unit 50 performs constant speed control when the motor torque is in the range of 0.4 N·m or less. Therefore, in automatic switching mode, even if the pushing force of the work implement is increased, the motor rotation speed is maintained constant as long as the motor torque is in the range of 0.4 N·m or less. When the motor torque exceeds 0.4 N·m, increasing the pushing force of the work implement increases the motor torque and decreases the motor rotation speed. Furthermore, the motor rotation speed decreases significantly before and after the coil connection method is switched from delta connection to star connection. Even in star connection, increasing the pushing force of the work implement increases the motor torque and decreases the motor rotation speed.

[0065] In the tenacity mode, there is no region of constant speed control, and when the pushing force of the work implement is increased, the motor torque increases and the motor rotation speed decreases.

[0066] 16 is a graph showing the relationship between the saw blade torque (torque of the rotation shaft of the saw blade 1309) and the saw blade rotation speed (rotation speed of the saw blade 1309) of the work machine 5 when the work machine pressing force is increased in both the automatic changeover mode and the tenacity mode. In this embodiment, as an example, the reduction ratio of the reduction mechanism is set to 3.88, the saw blade rotation speed is 1 / 3.88 of the motor rotation speed, and the saw blade torque is 3.88 times the motor torque.

[0067] 17 is a graph showing the relationship between the saw blade torque and saw blade rotation speed of the work implement 5 when the work implement pressing force is increased and then decreased in automatic switching mode. In automatic switching mode, the saw blade torque (4 N m or more) when the coil connection method is switched from delta connection to star connection is greater than the saw blade torque (2 N m or less) when the coil connection method is switched from star connection to delta connection. This is to prevent frequent switching between the delta connection and star connection.

[0068] 18 is a graph showing the relationship between the battery current effective value of the work implement 5 (effective value of the discharge current of the battery pack 1307) and the saw blade rotation speed when the work implement pressing force is increased and then decreased in the automatic switching mode. In the automatic switching mode, when the work implement pressing force is increased and the coil connection method is switched from the delta connection to the star connection, the battery current effective value drops sharply.

[0069] FIG. 19 is a control flowchart for the automatic changeover mode of the work implement 5, and is a control flowchart for when the work implement pressing force is gradually increased after the trigger switch 1306 is turned on.

[0070] When the trigger switch 1306 is turned on (S1), the calculation unit 50 turns on the delta connection relay element 32 (S3), turns off the star connection relay element 33 (S5), starts driving the inverter circuit 64 (S7), and drives the motor 340 (operates the work machine 5) with the coil connection method set to delta connection (S9). If the workload does not exceed the threshold A (No in S11), the calculation unit 50 continues driving the motor 340 in the delta connection.

[0071] When the workload exceeds threshold A (Yes in S11), the calculation unit 50 stops driving the inverter circuit 64 (S13), turns off the delta connection relay element 32 (S15), turns on the star connection relay element 33 (S17), resumes driving the inverter circuit 64 (S19), and drives the motor 340 with the coil connection method set to star connection (S21). Threshold A corresponds to the first winding switching threshold. The effective value of the motor current corresponding to threshold A is, for example, 60 A. Stopping the driving of the inverter circuit 64 means turning off all six switching elements that make up the inverter circuit 64.

[0072] FIG. 20 is a control flowchart for the automatic switching mode of the work implement 5, and is a control flowchart for when the work implement pressing force is gradually reduced during operation in star connection.

[0073] The calculation unit 50 drives the motor 340 in the star connection (S25), and if the workload is not equal to or less than the threshold B (No in S27), continues to drive the motor 340 in the star connection.

[0074] When the workload falls below threshold B (Yes in S27), the calculation unit 50 stops driving the inverter circuit 64 (S29), turns off the star connection relay element 33 (S31), turns on the delta connection relay element 32 (S33), resumes driving the inverter circuit 64 (S35), and drives the motor 340 with the coil connection method set to delta connection (S37). Threshold B corresponds to the second winding switching threshold. The aforementioned threshold A is greater than threshold B.

[0075] 21 is a control flowchart for the tenacity mode of the work machine 5. When the trigger switch 1306 is turned on (S41), the calculation unit 50 turns off the delta connection relay element 32 (S43), turns on the star connection relay element 33 (S45), starts driving the inverter circuit 64 (S47), and drives the motor 340 with the coil connection method set to star connection (S49).

[0076] 22 is a flowchart of overload protection control for the work machine 5. The calculation unit 50 drives the motor 340 in a star connection (S51), and if the workload does not exceed threshold C (No in S53), continues to drive the motor 340 in a star connection. If the workload exceeds threshold C (Yes in S53), the calculation unit 50 stops driving the inverter circuit 64 to stop the motor 340 (S55). Threshold C corresponds to the overload protection threshold. The effective value of the motor current corresponding to the overload protection threshold is, for example, 90 A. The aforementioned threshold A is equal to or less than threshold C, and is preferably equal to or greater than two-thirds of threshold C.

[0077] 23 is a flowchart of protection control in response to a discharge stop signal from the battery pack 1307 of the work machine 5. The premise of this flowchart is that the battery pack 1307 outputs a discharge stop signal (LD signal) when its own discharge current exceeds the battery-side overcurrent protection threshold.

[0078] The calculation unit 50 drives the motor 340 (S61), and if it does not receive a discharge stop signal from the battery pack 1307 (No in S63), it continues driving the motor 340. If it receives a discharge stop signal from the battery pack 1307 (Yes in S63), the calculation unit 50 stops driving the inverter circuit 64 and stops the motor 340 (S55).

[0079] As described above, the calculation unit 50 stops the motor 340 when the workload exceeds the threshold C. At this time, when the motor current exceeds the main body side overcurrent protection threshold, the calculation unit 50 determines that the workload has exceeded the threshold C. The battery side overcurrent protection threshold described above is greater than the main body side overcurrent protection threshold.

[0080] According to this embodiment, the following effects can be achieved.

[0081] (1) The calculation unit 50 is configured to be able to execute two modes: an automatic switching mode (first mode) in which the coil wiring method is switched from a delta connection for high rotation to a star connection (Y connection) for high torque in response to an increase in workload, and a tenacity mode (second mode) in which the coil wiring method is fixed to a star connection for high torque and the coil wiring method is not switched regardless of the workload. Therefore, unlike a mode in which the only mode is to switch the coil wiring method in response to the workload, it is possible to fix the coil wiring method regardless of the workload, which improves workability.

[0082] (2) In the tenacity mode, the calculation unit 50 sets the coil connection to a star connection for high torque. By setting the coil connection to a high torque connection from the beginning in this way, activation of the overload protection function due to the starting current after switching from a high rotation speed to a high torque mode can be suppressed, unlike when the coil connection is switched from a high rotation speed to a high torque mode midway.

[0083] (3) In the automatic switching mode, when the workload exceeds threshold A (first winding switching threshold), the calculation unit 50 switches the coil connection from a delta connection for high rotation to a star connection (Y connection) for high torque. Furthermore, when the workload exceeds threshold C (overload protection threshold), the calculation unit 50 stops the motor 340 using the overload protection function. Here, threshold A is set to be equal to or less than threshold C. This prevents the overload protection function from operating while the motor 340 is operating in a delta connection for high rotation, thereby improving workability. Furthermore, by setting threshold A to at least two-thirds of threshold C, the range in which the motor can operate at high rotation can be expanded, thereby improving workability. This effect can be maximized by setting threshold A equal to threshold C.

[0084] (4) The work implement 5 is provided with an operation mode selector switch 312 that allows the operator to select between the automatic changeover mode (first mode) and the tenacity mode (second mode) as the operation mode of the work implement 5. This allows the operator to freely select between the automatic changeover mode and the tenacity mode depending on the type of work to be performed, resulting in good workability.

[0085] (5) When switching the coil wiring method, the calculation unit 50 provides a pause period in which all six switching elements of the inverter circuit 64 are turned off. This prevents unexpected problems from occurring due to the inverter circuit 64 being driven while the coil wiring method is being switched, thereby improving reliability.

[0086] (6) In the automatic switching mode, when the coil wiring method is the star connection (Y connection) for high torque, and the workload decreases to below threshold B (second winding switching threshold), the calculation unit 50 switches the coil wiring method to the delta connection for high rotation. Here, threshold A (first winding switching threshold) is set to be larger than threshold B. This makes it possible to prevent the coil wiring method from being frequently switched between the delta connection and the star connection.

[0087] (7) When the battery pack 1307's own discharge current exceeds the battery-side overcurrent protection threshold, it outputs a discharge stop signal, and when the calculation unit 50 receives the discharge stop signal from the battery pack 1307, it stops the motor 340. On the other hand, when the motor current exceeds the main-body-side overcurrent protection threshold, the calculation unit 50 determines that the workload has exceeded threshold C and stops the motor 340. Here, the battery-side overcurrent protection threshold is greater than the main-body-side overcurrent protection threshold. Therefore, basically, the main-body-side overload protection function activates before the overcurrent protection function of the battery pack 1307 activates, thereby reducing the burden on the battery pack 1307.

[0088] (8) In connection switching control for switching the coil connection method from star connection to delta connection, i.e., in connection switching control for switching from a high-torque connection state to a high-speed connection state, when the inverter circuit 64 is in a drive-stop state, the calculation unit 50 is configured to switch from a state in which the delta connection relay element 32 is off and the star connection relay element 33 is on (high-torque connection state) to a state in which both the delta connection relay element 32 and the star connection relay element 33 are off (connection interruption state). Therefore, since the star connection relay element 33 is turned off when no current is flowing through it, the risk of damage to the star connection relay element 33 is reduced compared to when the star connection relay element 33 is turned off when current is flowing through it.

[0089] (9) In the connection switching control for switching the coil connection method from star connection to delta connection, when the inverter circuit 64 is in a drive-stop state, the calculation unit 50 is configured to switch from a state in which the delta connection relay element 32 and the star connection relay element 33 are both off (connection interruption state) to a state in which the delta connection relay element 32 is on and the star connection relay element 33 is off (high rotation speed connection state). Therefore, no current flows through the delta connection relay element 32 at the moment the delta connection relay element 32 is turned on, and the risk of damage to the delta connection relay element 32 is reduced.

[0090] 1 to 8 and 24 to 31 relate to a third embodiment of the present invention. Below, explanations of parts common to the first embodiment will be omitted as appropriate.

[0091] 24 is a graph showing time variations in the motor rotation speed, the output current of the battery pack 1307 (hereinafter referred to as "battery current"), and the duty of the PWM signal (hereinafter referred to as "duty") applied to each switching element (hereinafter referred to as "inverter FET") of the inverter circuit 64 in Control Example 1 of Embodiment 3. The battery current is substantially equal to the motor current.

[0092] When the trigger switch 1306 is turned on (motor drive operation) at time 0 seconds, the calculation unit 50 drives the motor 340 by increasing the duty from an initial value (e.g., 0%) at a first increasing rate (e.g., +7% / 10 ms) with the coil connection method set to delta connection. This reduces the starting current of the motor 340 and also suppresses product recoil compared to when the duty is rapidly increased. The calculation unit 50 performs constant speed control to set the motor rotation speed to a target value (e.g., 23,500 / min), so the duty is less than the maximum value (e.g., 100%) under no-load or light-load conditions. In constant speed control, the duty reaches its maximum value (around time 1.8 seconds) as the workload increases, and as the workload increases further, the motor rotation speed decreases (around time 1.8 to 2.5 seconds).

[0093] When the workload increases and a high-load condition (e.g., workload > threshold A) is met around time 2.5 seconds, the calculation unit 50 switches the coil connection from the delta connection to the star connection. At this time, the calculation unit 50 reduces the duty to an initial value (e.g., 0%), switches the coil connection from the delta connection to the star connection, and drives the motor 340 by increasing the duty at a second increasing rate greater than the first increasing rate. Increasing the duty at the second increasing rate is equivalent to, for example, a step-like increase in the duty from the initial value (e.g., 0%) to a maximum value (e.g., 100%). As a result, in the example of FIG. 24 , the rate of increase in the motor rotation speed when the motor 340 starts to drive (when the inverter circuit 64 starts to drive) is greater in the star connection (Y connection) than in the delta connection. Note that starting the drive of the motor 340 and the inverter circuit 64 includes restarting the drive, and the motor 340 may be rotating at the time of drive start.

[0094] After switching to the star connection, the calculation unit 50 drives the motor 340 with the duty set to the maximum value (e.g., 100%) (from time 2.5), and the motor rotation speed decreases as the workload increases. When the workload decreases and a low-load condition (e.g., workload≦threshold B) is met around time 4.1 seconds, the calculation unit 50 switches the coil connection from the star connection to the delta connection. At this time, the calculation unit 50 reduces the duty to an initial value (e.g., 0%), switches the coil connection from the star connection to the delta connection, and increases the duty in a stepwise manner from the initial value (e.g., 0%) to an intermediate value (e.g., 40%). Then, the calculation unit 50 increases the duty from the intermediate value (e.g., 40%) at a third increase rate (e.g., +8% / 10 ms) that is slower than the second increase rate, and drives the motor 340. The third increase rate (e.g., +8% / 10 ms) is faster than the first increase rate (e.g., +7% / 10 ms).

[0095] When the trigger switch 1306 turns off at 6 seconds, the calculation unit 50 initiates soft brake control. In soft brake control, all upper-arm switching elements of the inverter circuit 64 are turned off, and at least one lower-arm switching element of the inverter circuit 64 is PWM-controlled to gradually increase the duty. Gradually increasing the duty reduces the maximum value of the brake current and suppresses product recoil. Furthermore, compared to when the coil connection method is switched to a star connection to reduce the maximum value of the brake current before brake control is performed, the number of times the winding switching relay element 31 is switched on and off is reduced, thereby extending the life of the relay element 31. Soft brake control is performed when the trigger switch 1306 turns off in a delta connection state, but may not be performed when the trigger switch 1306 turns off in a star connection state. When the motor 340 stops, the calculation unit 50 sets the duty to 0%.

[0096] 25 is a flowchart of Control Example 1 of Embodiment 3. When trigger switch 1306 is turned on (S301), calculation unit 50 turns on delta connection relay element 32 (S303), turns off star connection relay element 33 (S305), starts driving inverter circuit 64 (S307), sets the electrical advance angle of the voltage applied to motor 340 (hereinafter referred to as the "electrical advance angle") to 40 degrees and the conduction angle of motor 340 (hereinafter referred to as the "conduction angle") to 120 degrees (S309), increases the duty from 0% at +7% every 10 ms (S311), and performs constant speed control of motor 340 with the coil connection method set to delta connection (S313).

[0097] If the workload does not exceed threshold A (No in S315), the calculation unit 50 continues driving the motor 340 in the delta connection. If the workload exceeds threshold A (Yes in S315), the calculation unit 50 stops driving the inverter circuit 64 (S317), turns off the delta connection relay element 32 (S319), turns on the star connection relay element 33 (S321), resumes driving the inverter circuit 64 (S323), immediately increases the duty from 0% to 100% (S325), and drives the motor 340 with the coil connection method set to star connection. Stopping the driving of the inverter circuit 64 means turning off all six switching elements that make up the inverter circuit 64.

[0098] If the workload is not equal to or less than threshold B (No in S327), the calculation unit 50 continues to drive the motor 340 in the star connection. If the workload becomes equal to or less than threshold B (Yes in S327), the calculation unit 50 stops driving the inverter circuit 64 (S329), turns off the star connection relay element 33 (S331), turns on the delta connection relay element 32 (S333), resumes driving the inverter circuit 64 (S335), immediately increases the duty from 0% to 40%, and then increases the duty from 40% by +8% every 10 ms (S337), and performs constant speed control of the motor 340 with the coil connection in the delta connection (S339). When the trigger switch 1306 is then turned off, the calculation unit 50 executes the soft brake control described above and then stops driving the inverter circuit 64.

[0099] 26 is a graph showing changes over time in motor rotation speed, battery current, duty, and electrical advance angle for Control Example 2 of the work machine of Embodiment 3, along with changes over time in Control Example 1. FIG. 27 is a flowchart of Control Example 2.

[0100] Control Example 2 differs from Control Example 1 in that the electrical lead angle when the motor 340 is driven in a star connection is set to, for example, 20 degrees, which is smaller than the electrical lead angle (for example, 40 degrees) when the motor 340 is driven in a delta connection, but is otherwise the same. The flowchart in Figure 27 is the same as the flowchart in Figure 25, except that it adds a process (S324a) of setting the electrical lead angle to 20 degrees after switching the coil connection method from the delta connection to the star connection, and a process (S336a) of setting the electrical lead angle to 40 degrees after switching the coil connection method from the star connection to the delta connection. Reducing the electrical lead angle in the star connection reduces the motor current in the star connection, preventing the motor 340 from stopping due to overcurrent protection.

[0101] 28 is a graph showing the motor rotation speed, battery current, time changes in duty, and time changes in conduction angle for Control Example 3 of the work machine of Embodiment 3, along with the time changes in Control Example 1. FIG. 29 is a flowchart of Control Example 3.

[0102] Control Example 3 differs from Control Example 1 in that the conduction angle when motor 340 is driven in a star connection is set to, for example, 120 degrees, which is smaller than the conduction angle (for example, 150 degrees) when motor 340 is driven in a delta connection, but otherwise is the same. The flowchart of FIG. 29 is similar to the flowchart of FIG. 25 except that the conduction angle after inverter circuit 64 starts driving (S307) is set to 150 degrees (S309b), and the following steps are added: a process of setting the conduction angle to 120 degrees after switching the coil connection from delta connection to star connection (S324b), and a process of setting the conduction angle to 150 degrees after switching the coil connection from star connection to delta connection (S336b). Reducing the conduction angle in the star connection reduces the motor current in the star connection, thereby preventing motor 340 from stopping due to overcurrent protection.

[0103] This embodiment has the following advantages.

[0104] (1) The calculation unit 50 controls the rate at which the duty is increased when the motor 340 starts to drive so that it is increased faster in a star connection (Y connection) than in a delta connection. Therefore, in a star connection, where the rise in motor rotation speed (startup of the motor 340) tends to be slower than in a delta connection at the same rate of increase in duty, the rise in motor rotation speed is made quicker, and a decrease in work speed is suppressed.

[0105] (2) When the trigger switch 1306 is operated to drive the motor, the calculation unit 50 drives the motor 340 by increasing the duty at a first increasing rate (e.g., +7% / 10 ms) with the coil connection in the delta connection. Thereafter, when the workload on the motor 340 increases, the calculation unit 50 reduces the duty, switches the coil connection from the delta connection to the star connection (Y connection), and increases the duty at a second increasing rate that is greater than the first increasing rate. This speeds up the motor rotation speed after the coil connection is switched from the delta connection to the star connection (Y connection). This improves workability (cutting speed) and tenacity during heavy-load work. In particular, when the motor 340 starts to operate after switching from the delta connection to the star connection (Y connection), a workload equal to or greater than the threshold A is applied. Therefore, if the duty remains low for a long period of time, the motor rotation speed decreases, causing overcurrent protection to activate and resulting in an unexpected stop of the motor 340. In this embodiment, by increasing the rate at which the duty increases after switching the coil connection method from the delta connection to the star connection (Y connection), the motor 340 rotation speed decreases immediately after switching, preventing the motor 340 from stopping due to overcurrent protection and thus preventing the motor 340 from stopping unexpectedly during work. This effect is more pronounced when the duty is rapidly increased from an initial value (e.g., 0%) to a maximum value (e.g., 100%) after switching the coil connection method from the delta connection to the star connection (Y connection).

[0106] (3) When the workload decreases while the motor 340 is being driven with the coil connection configured as star connection (Y connection), the calculation unit 50 is configured to reduce the duty, switch the coil connection from star connection (Y connection) to delta connection, and increase the duty at a third increase rate (e.g., +8% / 10 ms) that is lower than the second increase rate to drive the motor 340. Therefore, compared to when the third increase rate is the same as the second increase rate, the starting current of the motor 340 can be suppressed and product recoil can be suppressed after the coil connection is switched from star connection (Y connection) to delta connection.

[0107] (4) After switching the coil connection from star connection (Y connection) to delta connection, the calculation unit 50 rapidly increases the duty from an initial value (e.g., 0%) to an intermediate value (e.g., 40%). This allows the motor speed to rise more quickly after switching the coil connection from star connection (Y connection) to delta connection, and suppresses a decrease in operating speed, compared to when the duty is gradually increased from the initial value (e.g., 0%). Here, since the motor 340 is rotating at a speed equal to or greater than a certain level when it starts to operate after switching the coil connection from star connection (Y connection) to delta connection, rapidly increasing the duty to an intermediate value (e.g., 40%) does not cause an excessive increase in motor current, and the risk of overcurrent protection activation is limited.

[0108] (5) After the calculation unit 50 rapidly increases the duty to an intermediate value (e.g., 40%), the calculation unit 50 increases the duty at a third increase rate (e.g., +8% / 10 ms) greater than the first increase rate (e.g., +7% / 10 ms) to drive the motor 340. Therefore, compared to when the third increase rate is the same as the first increase rate, the motor speed increases more quickly (starting the motor 340) after switching the coil connection from star connection (Y connection) to delta connection, and a decrease in the operating speed is suppressed. When the motor 340 starts to operate after switching the coil connection from star connection (Y connection) to delta connection, the motor 340 is already rotating at a certain speed or higher. Therefore, the acceleration time until the motor speed reaches the target rotation speed for constant speed control is shorter than when the motor 340 starts to operate immediately after the trigger switch 1306 is operated to start the motor. Therefore, even if the third increase speed is greater than the first increase speed, the time during which the product recoil occurs is short, so that the deterioration of workability and feeling due to the recoil is suppressed.

[0109] (6) The calculation unit 50 is configured to be able to start driving the motor 340 in a plurality of drive modes with different duty increase rates during a single motor drive operation of the trigger switch 1306. Specifically, during a single motor drive operation of the trigger switch 1306, the calculation unit 50 executes the following: increasing the duty from the initial value at a first increasing rate; switching from the delta connection to the star connection (Y connection); increasing the duty from the initial value at a second increasing rate; switching from the star connection (Y connection) to the delta connection; and rapidly increasing the duty from the initial value to an intermediate value and then increasing the duty at a third increasing rate. This eliminates the need for the user to be aware of the operation of the trigger switch 1306, making the system easy to use.

[0110] (7) In control example 2, the calculation unit 50 sets the electrical advance angle when the motor 340 is driven in a star connection to, for example, 20 degrees, which is smaller than the electrical advance angle (for example, 40 degrees) when the motor 340 is driven in a delta connection. This reduces the motor current in the star connection, preventing the motor 340 from stopping due to overcurrent protection.

[0111] (8) In control example 3, the calculation unit 50 sets the conduction angle when the motor 340 is driven in a star connection to, for example, 120 degrees, which is smaller than the conduction angle (for example, 150 degrees) when the motor 340 is driven in a delta connection. This reduces the motor current in the star connection, preventing the motor 340 from stopping due to overcurrent protection.

[0112] FIG. 30 is a graph showing changes over time in motor rotation speed, battery current, and duty in Comparative Control Example 1 of Embodiment 3. Comparative Control Example 1 is a control example in which the second increase rate is set to the same as the first increase rate in Control Example 1. In this case, in the example of FIG. 30, after switching from delta connection to star connection, the increase rate of the duty is slow, so the motor rotation speed drops, the battery current rises sharply, the overcurrent protection is activated, and the motor 340 stops. Even if the motor 340 does not stop, the workability (cutting speed) decreases. Embodiment 3 is intended to suitably solve this problem of Comparative Control Example 1.

[0113] FIG. 31 is a graph showing the time changes in motor rotation speed, battery current, and duty in Comparative Control Example 2 of Embodiment 3, along with the time changes in Control Example 1. In Comparative Control Example 2, after switching the coil connection method from star connection (Y connection) to delta connection, the duty is not suddenly increased from the initial value (e.g., 0%) to an intermediate value (e.g., 40%), but is increased from the initial value (e.g., 0%) at a third increase rate, which is the same as the first increase rate. In this case, as shown in FIG. 31 , the increase in motor rotation speed is delayed after switching the coil connection method from star connection (Y connection) to delta connection, resulting in a long startup time and poor operability. Embodiment 3 is intended to effectively solve these problems of Comparative Control Example 2.

[0114] Control Examples 2 and 3 of Embodiment 3 may be combined with each other. That is, a combination of setting the electrical advance angle when motor 340 is driven in a star connection to be smaller than the electrical advance angle when motor 340 is driven in a delta connection and a combination of setting the conduction angle when motor 340 is driven in a star connection to be smaller than the conduction angle when motor 340 is driven in a delta connection may be used.

[0115] 1 to 8 and 32 to 36 relate to a fourth embodiment of the present invention. In Fig. 32 to 36, the time 0 seconds is the time when the motor drive operation is performed on the trigger switch 1306. Below, the description of the parts common to the first embodiment will be omitted as appropriate.

[0116] 32 is a graph showing time variations in motor rotation speed, battery current, and duty when the trigger switch 1306 is operated to drive the motor in the no-load state in each of the automatic switching mode and the tenacity mode, relating to control example 1 of the work machine of embodiment 4. The no-load state is a state in which no load is applied to the saw blade 1309, i.e., a state in which no external load is applied to the motor 340 (a state in which the work machine is not pressed against a mating material). In control example 1, when the trigger switch 1306 is operated to drive the motor, the electrical advance angle in the start-up control of the motor 340 is fixed at 40 degrees and the conduction angle is fixed at 120 degrees.

[0117] In the automatic switching mode, when the trigger switch 1306 is operated to drive the motor, the calculation unit 50 sets the coil connection method to delta connection and starts the motor 340. On the other hand, in the tenacity mode, when the trigger switch 1306 is operated to drive the motor, the calculation unit 50 sets the coil connection method to star connection and starts the motor 340.

[0118] The calculation unit 50 controls the duty increase rate (duty increase amount per unit time) in the startup control of the motor 340 when the trigger switch 1306 is operated to drive the motor in a no-load state so that it is larger when the coil wiring method is star connection (Y connection) (in tenacity mode) than when the coil wiring method is delta connection (in automatic switching mode). Specifically, the calculation unit 50 controls the duty increase rate in the startup control of the motor 340 when the trigger switch 1306 is operated to drive the motor in a no-load state so that it is +7% / 10 ms (corresponding to a first duty increase rate) when the coil wiring method is delta connection (in automatic switching mode), and +10% / 10 ms (corresponding to a second duty increase rate) when the coil wiring method is star connection (Y connection) (in tenacity mode). That is, when the trigger switch 1306 is operated to drive the motor under no-load conditions, the calculation unit 50 controls the motor so that the time from when the trigger switch 1306 is operated to when the duty cycle increases to a predetermined value (here, 100%) is shorter for the star connection than for the delta connection. As a result, the increase in motor rotation speed per unit time (hereinafter referred to as the "rotation speed increase rate") when the trigger switch 1306 is operated to drive the motor under no-load conditions is substantially equal between the delta connection coil connection (in the automatic switching mode) and the star connection (or Y connection) coil connection (in the tenacity mode), improving operability. Note that the decrease in duty cycle in the automatic switching mode from around 1.5 seconds in Figure 32 is due to the motor rotation speed approaching the target rotation speed for constant speed control. On the other hand, in the high-torque mode, even if the duty cycle is 100%, the motor rotation speed is below the target rotation speed for constant speed control, so the duty cycle remains constant at 100% after reaching 100%.

[0119] 33 is a flowchart of control example 1 of embodiment 9. The calculation unit 50 controls the driving of the motor 340 in the operation mode (automatic switching mode or tenacity mode) selected by the operation mode changeover switch 312 (S350).

[0120] In the automatic switching mode ("automatic switching mode" in S350), the calculation unit 50 turns on the delta connection relay element 32 (S351) and turns off the star connection relay element 33 (S353). When the trigger switch 1306 turns on (S355), the calculation unit 50 starts driving the inverter circuit 64 (S357), sets the electrical advance angle to 40 degrees and the conduction angle to 120 degrees (S359), and increases the duty from 0% at +7% / 10 ms (S361).

[0121] In the tenacity mode ("tenacity mode" in S350), the calculation unit 50 turns off the delta connection relay element 32 (S363), turns on the star connection relay element 33 (S365), and when the trigger switch 1306 turns on (S367), starts driving the inverter circuit 64 (S369), sets the electrical advance angle to 40 degrees and the conduction angle to 120 degrees (S371), and increases the duty from 0% at +10% / 10 ms (S373).

[0122] In control example 1, when the trigger switch 1306 is operated to start the motor 340 in an unloaded state, the calculation unit 50 controls the duty increase rate so that it is greater in star connection than in delta connection. As a result, the rotation speed increase rate, which is the increase in motor rotation speed per unit time, is equivalent between delta connection and star connection, improving workability. Regarding the rotation speed increase rate, "equivalent" does not necessarily mean that the rotation speed increase rates are the same, but may differ within a range that provides the same user experience, including, for example, a difference of less than 10%. The user experience also includes the way the sound is perceived.

[0123] Since the speed of rotation increase is equivalent between the delta connection and the star connection, the speed of motor current also increases. On the other hand, the speed of the motor at 100% duty and no load is lower in the star connection than in the delta connection. Therefore, when starting the motor under no load, the maximum motor current in the star connection is smaller than the maximum motor current in the delta connection. Therefore, in the star connection, from the perspective of the maximum motor current during no load motor startup, there is room to further increase the duty increase rate and increase the speed of rotation faster than in the delta connection. However, in this embodiment, the speed of rotation increase in the star connection is kept approximately the same as that in the delta connection, thereby suppressing recoil during motor startup and providing a feeling equivalent to that of the delta connection, thereby improving operability.

[0124] In the example of FIG. 32 , the duty increase rate is set to be greater in the star connection than in the delta connection throughout the entire period until the duty reaches 100%. However, the duty increase rate may be slower in the star connection than in the delta connection during part of the period until the duty reaches 100%. That is, when the trigger switch 1306 is operated to start the motor 340 in an unloaded state, the calculation unit 50 may control the duty increase rate to be greater in the star connection than in the delta connection. Alternatively, the calculation unit 50 may control the time average value of the duty increase rate until the duty reaches 100% to be greater in the star connection than in the delta connection. Regardless of whether this has technical significance, the scope of Control Example 1 also includes, for example, a case where the duty increase rate is momentarily slower in the star connection than in the delta connection.

[0125] 34 is a graph showing changes over time in motor rotation speed, battery current, and electrical advance angle when the trigger switch 1306 is operated to drive the motor in the no-load state in each of the automatic changeover mode and the tenacity mode, relating to control example 2 of the work machine of embodiment 4. In control example 2, when the trigger switch 1306 is operated to drive the motor, the duty increase rate in the start-up control of the motor 340 is fixed at +7% / 10 ms, and the conduction angle is fixed at 120 degrees.

[0126] The calculation unit 50 controls the electrical advance angle when the trigger switch 1306 is operated to drive the motor in a no-load state so that it is larger when the coil wiring method is star connection (Y connection) (in tenacity mode) than when the coil wiring method is delta connection (in automatic switching mode). Specifically, the calculation unit 50 controls the electrical advance angle when the trigger switch 1306 is operated to drive the motor in a no-load state so that it is, for example, 40 degrees when the coil wiring method is delta connection (in automatic switching mode) and is, for example, 60 degrees when the coil wiring method is star connection (Y connection) (in tenacity mode). As a result, the rate of increase in rotation speed when the trigger switch 1306 is operated to drive the motor in a no-load state is substantially equal when the coil wiring method is delta connection (in automatic switching mode) and when the coil wiring method is star connection (Y connection) (in tenacity mode), improving operability.

[0127] In Control Example 2 of Embodiment 4, when the coil wiring method is star connection (Y connection), for example, after the duty cycle has increased to a maximum (for example, 100%), the electrical advance angle may be reduced to, for example, 40 degrees or 20 degrees.

[0128] 35 is a graph showing changes over time in motor rotation speed, battery current, and conduction angle when the trigger switch 1306 is operated to drive the motor in the no-load state in each of the automatic changeover mode and the tenacity mode, relating to control example 3 of the work machine of embodiment 4. In control example 3, when the trigger switch 1306 is operated to drive the motor in the no-load state, the duty increase rate in the start-up control of the motor 340 is fixed at +7% / 10 ms, and the electrical advance angle is fixed at 40 degrees.

[0129] The calculation unit 50 controls the conduction angle when the trigger switch 1306 is operated to drive the motor in the no-load state so that it is larger when the coil wiring method is star connection (Y connection) (in tenacity mode) than when the coil wiring method is delta connection (in automatic switching mode). Specifically, the calculation unit 50 controls the conduction angle when the trigger switch 1306 is operated to drive the motor in the no-load state so that it is, for example, 120 degrees when the coil wiring method is delta connection (in automatic switching mode) and 150 degrees when the coil wiring method is star connection (Y connection) (in tenacity mode). As a result, the rate of increase in the rotation speed when the trigger switch 1306 is operated to drive the motor in the no-load state is substantially equal when the coil wiring method is delta connection (in automatic switching mode) and when the coil wiring method is star connection (Y connection) (in tenacity mode), improving operability.

[0130] In Control Example 3 of Embodiment 4, when the coil wiring method is star connection (Y connection), for example, after the duty is increased to a maximum (for example, 100%), the conduction angle may be reduced to, for example, 120 degrees.

[0131] Control Examples 1 to 3 of Embodiment 4 may be combined with one another. That is, the calculation unit 50 may control two or more of the duty increase rate, the electrical advance angle, and the conduction angle when the trigger switch 1306 is operated to drive the motor in a no-load state so that they are larger when the coil wiring method is star connection (Y connection) (in tenacity mode) than when the coil wiring method is delta connection (in automatic switching mode).

[0132] In the control examples 1 to 3 of the fourth embodiment, the calculation unit 50 may control the rotation speed increase rate when the trigger switch 1306 is operated to drive the motor in an unloaded state by increasing at least one of the duty increase rate, electrical advance angle, and conduction angle when the coil connection is star-connected (Y-connected). This may increase the rotation speed when the coil connection is star-connected (Y-connected) (in tenacity mode) compared to when the coil connection is delta-connected (in automatic switching mode). This increases product recoil when the coil connection is star-connected (Y-connected), but shortens the startup time. Because a star connection allows less battery current to flow than a delta connection, increasing the rotation speed increase rate in the star connection does not result in an excessively large startup current. The settings may be adjusted appropriately based on the type of work machine and the nature of the work, taking into account the balance between the battery current that can be flowed in the star connection, the product recoil, and the startup time.

[0133] 36 is a graph showing the time variations in motor rotation speed, battery current, and duty when the trigger switch 1306 is operated to drive the motor under no-load conditions in each of the automatic switching mode and the tenacity mode, relating to a comparative control example of embodiment 4. In the comparative control example, the duty increase rate in the startup control of the motor 340 under no-load conditions when the trigger switch 1306 is operated to drive the motor under no-load conditions in Control Example 1 is set to +7% / 10 ms both when the coil connection is star-connected (Y-connected) (tenacity mode) and when the coil connection is delta-connected (automatic switching mode). In the comparative control example, the rate of increase in rotation speed under no-load conditions when the trigger switch 1306 is operated to drive the motor under no-load conditions is smaller when the coil connection is star-connected (Y-connected) (tenacity mode) than when the coil connection is delta-connected (automatic switching mode). That is, in the comparative control example, when the coil connection method is star connection (Y connection) (in tenacity mode), the start-up time of the motor 340 becomes long, resulting in poor workability. The ninth embodiment is intended to suitably solve this problem of the comparative control example.

[0134] Although the present invention has been described above using the embodiments as examples, the present invention is not limited to the embodiments. Various modifications can be made to the details specifically described in the embodiments within the scope of the claims.

[0135] In the first and third embodiments, the operation mode may be the automatic switching mode only. In this case, the operation mode switching switch 312 and the operation mode display LED 313 may be omitted.

[0136] From another perspective, switching the coil wiring method is switching the internal resistance of the motor 340 or the internal resistance of the stator coil 345 (hereinafter referred to as "internal resistance"). That is, when the trigger switch 1306 is operated to drive the motor under no load, the calculation unit 50 is configured to start the motor 340 in one of a first state in which the internal resistance is low (e.g., a state in which the coil wiring method is delta-connected) and a second state in which the internal resistance is high (e.g., a state in which the coil wiring method is star-connected). In control example 1 of embodiment 9, the calculation unit 50 is configured to control the duty increase rate so that it is higher in the second state than in the first state. As shown in FIG. 37 , the two-phase resistance of a delta connection, for example, between a-b, is the combined parallel resistance of the resistances of the series-connected W-phase and V-phase stator coils and the resistance of the U-phase stator coil. As shown in FIG. 38 , the two-phase resistance in a star connection, for example, between a and b, is the combined series resistance of the U-phase stator coil and the V-phase stator coil, which is greater than the two-phase resistance in a delta connection. Note that switching the coil connection method may involve changing the number of series or parallel connections of coils in each phase. For example, in a star connection in which the number of series connections in each phase is variable as shown in FIG. 39 , the two-phase resistance when the number of series connections is two, for example, between a and b, is the combined series resistance of the two U-phase stator coils and the two V-phase stator coils (a total of four stator coils). When the number of series connections is one, for example, between a and b, is the combined series resistance of the one U-phase stator coil and the one V-phase stator coil (a total of two stator coils). The state with one series connection corresponds to the first state, and the state with two series connections corresponds to the second state.

[0137] The motor current, motor rotation speed, motor torque, battery current, saw blade rotation speed, saw blade torque, time, various voltages (inverter voltage, rated voltage, allowable voltage, etc.), rated capacity, duty, electrical advance angle, conduction angle, current ranges and number of time thresholds for each winding switching condition and overcurrent protection activation condition, etc., which are given as examples of specific numerical values ​​in the embodiments, do not in any way limit the scope of the invention and can be changed as desired to suit the required specifications.

[0138] The working machine of the present invention is not limited to a portable circular saw, but may be other types of cutting machines such as a bench circular saw, a rotary band saw, a jigsaw, a saber saw (reciprocating saw), a brush cutter, etc. The working machine of the present invention may also be a grinding machine having a grinding tip tool such as a grinder, a polishing machine having a polishing tip tool such as a sander or a polisher, a cutting machine having a cutting tip tool such as a plane, a trimmer or a router, a drilling machine having a drilling tip tool such as a drill, a hammer or an earth auger, a tightening machine having a tightening tip tool such as an impact driver, an impact wrench, a driver drill, a shear wrench, a riveter or a rebar tying machine, a crimping machine having a crimping tip tool such as a crimping machine, a bending machine having a bending tip tool such as a rebar bender, or a driving machine having a driving tip tool such as a nail gun or a tacker.

[0139] 5...Work machine, 50...Calculation unit (control unit), 51...Control power supply circuit (control circuit voltage supply circuit), 52...Current detection circuit (motor current detection circuit), 53...Switch operation detection circuit, 54...Battery type detection circuit, 55...Voltage detection circuit (battery voltage detection circuit), 56...Control signal circuit (control signal output circuit), 57...Rotation position detection circuit (rotor position detection circuit), 58...Rotation speed detection circuit, 59...Operation mode detection circuit, 61...Illumination LED drive circuit, 62...Illumination LED, 63...Hall IC (magnetic sensor), 64...Inverter circuit, 65...Detection resistor, 66...LD detection circuit, 67...Battery cell, 68...Protection IC (battery side control unit), 69...Battery temperature detection circuit, 70...Thermistor (temperature detection element), 71...Circuit temperature detection circuit, 72...Upper switching element, 73...Lower switching element, 74...Control circuit voltage detection circuit, 75...display LED drive circuit, 76...winding switching operation output circuit, 312...operation mode selector switch, 313...operation mode display LED, 314...light mode selector switch, 315...light mode display LED, 317...light mode display LED, 340...motor, 341...motor shaft, 342...rotor core, 343...rotor magnet (permanent magnet), 344...stator core, 345...stator coil, 346...yoke portion, 347...teeth (teeth portion), 1306...trigger switch, 1307...battery pack, 1309...saw blade, 1311...control board, 1316...operation panel, 1320...housing, 1321...motor housing, 1322...handle housing, 1323...battery attachment portion, 1324...hook, 1325...gear case (saw cover), 1326...sub-handle.

Claims

1. A work machine comprising: a motor having multiple windings; a drive unit having switching elements for driving the motor; a connection switching unit capable of switching the connection method of the multiple windings between a first connection method for high rotation and a second connection method for high torque; a control unit for controlling the drive unit and the connection switching unit; and an operation unit for starting and stopping the motor, wherein the control unit is configured to control the increase speed, which is the increase per unit time of the duty of the PWM signal applied to the switching element when the motor starts to be driven, so that it is in a state where it is greater when the second wiring method is used than when the first wiring method is used.

2. A work machine as described in claim 1, characterized in that, when a motor driving operation is performed on the operating unit, the control unit is configured to drive the motor by increasing the duty at a first increasing speed with the wiring method set to the first wiring method, and thereafter, when the work load applied to the motor increases, the control unit reduces the duty, switches the wiring method from the first wiring method to the second wiring method, and drives the motor by increasing the duty at a second increasing speed that is greater than the first increasing speed.

3. A work machine as claimed in claim 2, characterized in that increasing the duty at the second increasing speed is increasing the duty in a stepwise manner or abruptly increasing the duty to a maximum value.

4. A work machine as described in claim 2, characterized in that the control unit is configured to, when the work load becomes smaller while the motor is being driven with the wiring method set to the second wiring method, reduce the duty, switch the wiring method from the second wiring method to the first wiring method, and increase the duty at a third increase speed which is smaller than the second increase speed to drive the motor.

5. A work machine as claimed in claim 4, characterized in that the control unit is configured to switch the wiring method from the second wiring method to the first wiring method, and then rapidly increase the duty to an intermediate value and increase it from the intermediate value at the third increasing speed.

6. A work machine according to claim 4 or 5, characterized in that the third increased speed is greater than the first increased speed.

7. A work machine as described in claim 1, characterized in that the control unit is configured to be able to start driving the motor in a plurality of driving modes in which the duty increase speed differs during a single motor driving operation of the operating unit.

8. A work machine as described in claim 1, characterized in that the control unit controls at least one of the advance angle of the voltage applied to the motor and the current angle of the motor so that it is larger when the first wiring method is used than when the second wiring method is used.

9. A work machine as claimed in claim 1, comprising a tool holder driven by the motor, and the control unit is configured to control the motor so that when the operating unit is operated to start the motor in an unloaded state where no load is applied to the tool attached to the tool holder, the increasing speed is greater in the second wiring method than in the first wiring method.

10. A work machine as claimed in claim 1, comprising a tool holder driven by the motor, wherein the control unit is configured to start the motor by one of the first wiring method and the second wiring method when the operating unit is operated in an unloaded state where no load is applied to the tool attached to the tool holder, and wherein the control unit is configured to control the increasing speed so that, when the operating unit is operated in the unloaded state, the increasing speed is a first duty increasing speed when the motor is started by the first wiring method, and a second duty increasing speed when the motor is started by the second wiring method, and the second duty increasing speed is greater than the first duty increasing speed.

11. A work machine as claimed in claim 1, comprising a tool holder driven by the motor, wherein the control unit is configured to start the motor by one of the first wiring method and the second wiring method when the operating unit is operated in an unloaded state where no load is applied to the tool attached to the tool holder, and wherein the control unit is configured to control the motor so that, when the operating unit is operated in the unloaded state, the time from when the operating unit is operated to when the duty of the PWM signal applied to the switching element increases to a predetermined value is shorter in the second wiring method than in the first wiring method.

12. A work machine as claimed in any one of claims 9 to 11, characterized in that, when the operating part is operated in the no-load state, the rate of increase in the motor's rotation speed, which is the increase per unit time in the motor's rotation speed, is equivalent in the first wiring method and in the second wiring method.

13. A work machine comprising: a motor having a plurality of windings; a drive unit having switching elements for driving the motor; a connection switching unit capable of switching the connection method of the plurality of windings between a first connection method for high rotation and a second connection method for high torque; a control unit for controlling the drive unit and the connection switching unit; and an operation unit for starting and stopping the motor, wherein the control unit controls the rate of increase in the rotation speed of the motor when the motor begins to be driven so that it is greater when the second connection method is used than when the first connection method is used.

14. A working machine as claimed in any one of claims 1, 9 to 11 and 13, characterized in that it is configured to be able to select one of a first mode in which the wiring method is switched from the first wiring method to the second wiring method as the load applied to the motor increases, and a second mode in which the wiring method remains the second wiring method regardless of the load.

15. A work machine comprising: a motor having a plurality of windings; a tool holder driven by said motor; a drive unit having a switching element and driving said motor; a switch unit capable of changing the internal resistance of the plurality of windings; a control unit controlling said drive unit and said connection switch unit; and an operation unit for operating start and stop of said motor, wherein said control unit is configured to start the motor in one of a first state in which the internal resistance is low and a second state in which the internal resistance is high when said operation unit is operated in an unloaded state in which no load is applied to a tool attached to said tool holder, and said control unit is configured to control a duty increase speed, which is an increase per unit time in the duty of a PWM signal applied to the switching element, so that it is greater in the second state than in the first state when the operation unit is operated in the unloaded state to start the motor.

16. A working machine as described in claim 15, characterized in that the first state is a state in which the connection method of the multiple windings is a first connection method for high rotation, the second state is a state in which the connection method is a second connection method for high torque, and the switching unit is capable of switching the connection method between the first connection method and the second connection method.

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